Written by Matthew Archer.
The titan intelligence researcher Arthur Jensen once told Charles Murray that he wouldn’t pay five cents to raise his IQ 5 points. Why? Because a 5 point difference doesn’t seem to predict anything of importance when it comes to individual life outcomes. If you have some basic statistical knowledge—like what standard deviation is and why it’s more useful than percentages for such discussions—this should be an interesting statement.
The reason being that a 5 point IQ difference translates into wildly different positions on the bell curve depending on where you start. Take someone at IQ 100 (the normed mean), IQ 105 now places them at the 63rd percentile, IQ 120 is the 90th percentile, IQ 125 is the 95th percentile, IQ 130 = 97.7th percentile, IQ 135 = 99th percentile. You get the idea. That’s why Jensen’s statement is somewhat counterintuitive. One would assume that lower down the distribution 5 IQ points could really make a difference.
Then throw into the mix Murray and Herrnstein’s remark in The Bell Curve (page 367) that raising the mean IQ from 100 to 103 would get you the following:
For starters, the poverty rate falls by 25 percent. So does the proportion of males ever interviewed in jail. High school dropouts fall by 28 percent. Children living without their parents fall by 20 percent. Welfare recipiency, both temporary and chronic, falls by 18 percent. Children born out of wedlock drop by 15 percent. The incidence of low-weight births drops by 12 percent. Children in the bottom decile of home environments drop by 13 percent. Children who live in poverty for the first three years of their lives drop by 20 percent.
So small gains at the level of populations can generate immense changes for individuals, while small-moderate gains for individuals don’t seem to do much. This isn’t that surprising when you consider that, in Jensen’s words, ‘getting just one additional correct item on the Ravens makes for two to three points increase in IQ’. Put that way, would we really expect to see much of a difference in life outcomes because somebody could do two extra questions like this:
Probably not.
Another go-to reference here is Gottfredson’s 1997 article, Why g Matters: The complexity of everyday life. She mentions the vast range of ability for those in work:
Job incumbents, in turn, are more homogeneous than applicants: the SD of job incumbents on ability tests is .6 to .7 of that for applicants (Hunter, Schmidt, & Judiesch, 1990)-but they still range widely in ability. Translating these data into the IQ metric, the average SD among incumbents in an occupation is between about 7.5 and 8.7 IQ points (compared with 15 for the general population). This means that two thirds of incumbents in the average job fall within a range of 15 to 17 IQ points; over 95% would be within a range of 30 to 34 points.
In other words, there’s a lot more to job success (once you reach a certain threshold) than a few extra IQ points. Hence the lack of predictive power for key life outcomes when it’s just a handful of points.
And yet I still can’t shake the idea that Jensen’s remark was hyperbole, something Murray agrees with. This isn’t to say such a gain wouldn’t indeed be minimal, but a minimal gain at the right tail could be a more moderate gain at the left. Although my own reading of the data suggests that diminishing marginal returns seem to be something of a myth anyway. For example, David Lubinski details how extra IQ points still predict creative achievement in the top 1% of ability, even amongst a group where qualifications and university prestige is controlled for, say MIT physics graduates. Regardless, perhaps we simply don’t have the level of measurement precision to declare that an extra 5 IQ points for someone sitting at IQ 80 wouldn’t be significant. After all, it’s around this level that the US Army cut-off point comes into play and where most jobs are too difficult for you to be worth paying. Not to mention that 5 IQ points can be a matter of life and death.
So if anybody’s selling 5 IQ points, I’m buying.
Postscript:
Perhaps there is a 5 point IQ pill. From the Wiki for dexedrine:
One review highlighted a nine-month randomized controlled trial of amphetamine treatment for ADHD in children that found an average increase of 4.5 IQ points, continued increases in attention, and continued decreases in disruptive behaviors and hyperactivity
Matthew Archer is the Editor-in-Chief of Aporia.
Would you pay 5 cents for 5 IQ points?